HP-67 Low battery LED lights randomly

[Danito-Danone]

Hi fellows,

My HP-67 works fine, but the low battery LED comes on randomly on even when the machine is doing nothing and voltage is 3.6V or more. Could it be a defective capacitor? Thanks. D-D

[teenix]

(02-05-2023 01:12 AM)Danito-Danone Wrote:  Hi fellows,

My HP-67 works fine, but the low battery LED comes on randomly on even when the machine is doing nothing and voltage is 3.6V or more. Could it be a defective capacitor? Thanks. D-D

The low battery LED is controlled by the LLD input (pin 14) of the cathode driver IC.

Internally it measures the battery voltage and if it goes below a certain point, the LED will start to turn on.

You might like to check your battery connections and wiring to the keyboard and interconnections between the keyboard and CPU board for corrosion. Also check the wiring where it solders onto the keyboard as with over handling while disassembled, the wire ends can fray. See page 39 of my Classic Notes.

As the battery power goes through the on/off switch, the contacts may be dirty especially from any original switch lube put on by the factory which may have deteriorated over the years.

Gently wiggling the switch or wiring or CPU board may reveal a problem with the LED coming on.

cheers

Tony

[Danito-Danone]

Many thanks Tony! D-D